Recent advances in touch-screen technology and artificial skins for robotics and prosthetics are increasing the demand for interactivity with human users. Haptic interfaces are the most important sensory feedback, after the visual feedback, allowing users to receive a tactile response to varying shapes and textures. The most common technologies for haptic interfaces today are based on either (i) electrostatic forces, used to control friction between a user's finger and a screen, or (ii) ultrasonically excited flexural waves, traveling on an elastic, uniform screen. However, the spatial resolution achievable and the force output reachable by such technologies remains limited.
A grid of connected actuators can achieve a complex tactile pattern. However, providing power and control for such a grid is a very challenging problem. In addition, most haptic actuators can be divided into two categories; bulky and powerful such as acoustic coils or thin and weak such as piezoelectric actuators. Moreover, most actuators are limited to a single polarization excitation (e.g., out-of-plane or in-plane). Therefore, the need for flexible, thin, yet scalable amplification mechanisms is apparent.